Colorectal Cancer and Screening Flashcards
What are the causes of colorectal cancer?
Most cases (85%) sporadic
Some have a familial risk
IBD
What are the risk factors for sporadic cases of colorectal cancer?
Age Male sex Previous adenoma Obesity Poor diet Lack of exercise Smoking Diabetes mellitus
What are colorectal polyps?
Proturberent growths
Variety of histological types
Majority of colorectal cancers arise from pre-existing polyps
What gene processes need to take place for a colorectal adenoma to progress to a carcinoma?
Activation of an oncogene- k-ras or c-myc
Loss of tumour suppressor gene- p53, APC or DCC
Defective DNA repair pathway genes
How does colorectal cancer present?
Rectal bleeding
Altered bowel habits and loose stool >4 weeks
Iron deficiency anaemia
Palpable rectal or right lower abdominal mass
Possible acute colonic obstruction
Systemic symptoms of malignancy
What is the investigation of choice in suspected cases of colorectal cancer and why?
Colonoscopy
Allows tissue biopsies to be taken and can also be therapeutic (polyp removal)
What investigations are useful in the staging of colorectal cancer?
CT Chest/Abdo/Pelvis
MRI for rectal tumours
PET scan
Rectal endoscopic ultrasound
Describe the TNM staging of colorectal cancer
T1- confined to submucosa
T2- confined to muscularis
T3- confined to serosa
T4- breached serosa (invading other structure T4a, perforating bowel T4b)
N1- tumour seen in up to 3 regional lymph nodes
N2- tumour seen in 4+ regional lymph nodes
M1- metasases to distant organs
Describe the treatment of colorectal cancer
Basis of treatment is surgery
Can be endoscopic polyp removal, laparotomy, stoma formation
Chemotherapy can be adjuvant
Radiotherapy only helpful in cases of rectal cancer, and must be neoadjuvant to surgery
Describe possible palliative measures in cases of colorectal cancer
Chemotherapy and colonic stenting
Describe screening measures for colorectal cancer
Faecal occult blood test done every two years in everyone aged 50-74, if FOBT positive, refer for colonoscopy. Change to FIT testing in 2017
Further screening offered to high risk groups
What is FAP and what causes it?
An autosomal dominant condition caused by mutation of the APC gene on chromosome 5
Leads to multiple (>100) adenomas throughout the colon
Describe the interventions indicated in cases of FAP
Annual colonoscopy from 10/12 years up
Prophylactic proctocolectomy usually by age 16-25
What is HNPCC and what causes it?
An autosomal dominant condition caused by mutation of the DNA mismatch repair genes
Causes early onset CRC
Describe the interventions indicated in cases of HNPCC
Screening from age 25 with a 2 yearly colonoscopy
